Derivatization of amino acids by fungal laccases: Comparison of enzymatic and chemical methods

Derivatization of the unprotected amino acids L-phenylalanine and L-tryptophan can be achieved by laccase-catalyzed cross linking to para-dihydroxylated compounds. The use of amino acids in laccase-catalyzed aminations may provide the basis of new adhesives modeled on mussel adhesive proteins. We have used laccases from Pycnoporus cinnabarinus and Myceliophthora thermophila for the enzymatic derivatization and compared its effectiveness to chemical catalysis by sodium iodate. Both types of catalysis resulted in the formation of mono- or diaminated products, depending on the degree of substitution of the dihydroxylated substances. However there were considerable differences in the courses of the chemically and enzymatically catalyzed reactions. Thus, the laccase-catalyzed reaction of 2,5-dihydroxyacetophenone with L-phenylalanine and L-tryptophan resulted in mono- and diaminated coupling products (yields 40–60%) while no transformation products were recovered from the reaction catalyzed by 6 mM sodium iodate. In this case the laccase-catalyzed derivatization is clearly more efficient than the chemically catalyzed counterpart.